If the previous patent has been authorized, if the modified product wants to protect the improved part, it should apply for a new patent. Only in this way can we form tighter protection. Because the former patent protects product A, the latter patent protects the improved technical scheme B on product A, and the scope of protection is different.
If the previous patent is not authorized, the improvement made in the previous patent application date 12 months can be re-applied for a patent, claiming the priority of the previous patent, then the previous patent will be withdrawn, and the re-applied patent will obtain a relatively perfect protection scope of A+B.